1. Field of the Invention
The present invention is directed to adhesively securable and/or matingly sealable stock materials having a pre-applied, encapsulated adhesive or sealant composition wherein the pre-applied, encapsulated adhesive and sealant composition resist premature activation, even with the application of pressures typical for fracturing traditional encapsulated adhesives and sealants. In particular, the present invention is directed to stock materials having applied thereto a pre-applied encapsulated, liquid adhesive or sealant composition wherein at least one curative ingredient necessary for effectuating polymerization or cure of the adhesive or sealant composition is contained within a non-liquid, non-flowing carrier material that is encapsulated. In a preferred embodiment, the present invention is directed to stock materials having threaded elements for fastening including fasteners, conduits and finished stock materials to be assembled into a larger apparatus or assembly; utilized in retaining or blind hole bonding applications, and other stock materials having a planar surface for bonding applications as well as stock packaging materials, especially paperboard packages and containers.
2. Description of Related Art
Adhesive and sealant compositions are available in a seemingly endless variety of chemistries, forms (whether as a state of being or physical construct) and mechanisms of cure or polymerization. The types of chemistries include epoxies, urethanes, acrylic esters, vinyl esters, polyesters, polyvinylacetates, etc. Their physical state may be that of a water-like liquid, a viscous flowable or non-flowable material, a solid or semi-solid form, etc. Water-like liquid forms may comprise one or more liquid curable or polymerizable monomers, oligomers and/or prepolymers or a solid or semi-solid material that is dissolved in an appropriate solvent. Viscous forms may be highly thickened compositions; particularly those liquid systems that further contain thixotropic agents or other thickening fillers and polymeric materials. Solid and semi-solid compositions include temperature sensitive materials, such as hot melts and reactivatable adhesives, as well as materials that, due to their inherent characteristics or the presence of tackifiers and/or plasticizers, are sticky in nature, such as pressure sensitive adhesives.
Curable adhesive and sealant compositions also vary widely in their physical construct. They may exist as true one-part systems where all components necessary for effectuating the bond or seal are present in the adhesive or sealant composition, e.g., anaerobic adhesive and sealants or solvent type adhesives and sealants. Alternatively, they exist as two- or more part systems wherein each part is kept separated or isolated from the other until time of use. These too take many forms. The simplest form, oftentimes employed with two-part epoxy systems, is that where semi-solid beads of each component are extruded in a side-by-side relationship, with or without a tape backing or support. A more complex form is that where a special packaging design is employed to keep the reactive components isolated from each other until the time of use, e.g., a dual barrel or a single barrel, dual compartment caulking-type tube, a mixer cup which has separate compartments which collapse to form a single compartment upon use or a self-contained packaging wherein both a crushable ampule (often glass) containing one component and the liquid curable component are contained in a single container which is made of a flexible material so as to allow for the crushing of the ampule and the kneading of the two components before dispensing. A particularly successful and desirable form of two- or more-part adhesives and sealants are those known as encapsulated adhesives and sealants wherein one or more curative components are isolated from the remaining components through encapsulation, more specifically microencapsulation.
The mechanism of cure or polymerization for the various adhesive and sealants vary widely as well. Solvent based adhesives and sealants are effectively “cured” upon evaporation of the solvent carrier. Monomeric, oligomeric and/or pre-polymeric adhesive and sealant systems may cure or polymerize through step growth polymerization and/or addition polymerization, especially free radical, cationic or anionic polymerization, each of which may be facilitated by or initiated chemically or by environmental conditions including heat and/or light. Other systems, especially pre-polymeric and polymeric systems may cure through cross-linking with other monomers, oligomers and or prepolymers.
With such a variety of adhesive and sealant compositions, it is no wonder that they find broad use across a number of industries as well as in the construction and consumer markets. While there are so many different choices of adhesive and sealant chemistries, forms and mechanisms of cure or polymerization, no one is suitable for all applications. Each has attributes and characteristics, both of the uncured system and of the cured adhesive or sealant that will dictate where and when any given system or composition may be used. For example, solvent based adhesives are fine for making adhesive tapes, flooring bonding systems, wood glues and other consumer glues; however, such adhesive and sealant systems are not useful for most industrial assembly operations due to environmental and safety concerns with the solvents, especially organic solvents, nor for applications where speed of cure is important.
While many different adhesive and sealant compositions find utility in industrial manufacture and assembly operations, selection of the appropriate adhesive and sealant is particularly important. Although hot melt type adhesives probably account for the greatest volume of adhesives used in manufacturing, liquid curable adhesives and sealants have more applications and provide far greater versatility in industrial applications. The most common form of liquid curable adhesive and sealants used in industrial manufacture and assembly operations are the one-part systems. However, multi-part liquid adhesive and sealant compositions also find use; although these require the use of more sophisticated application means so that mixing occurs concurrent with dispensing. Since mixing typically initiates curing or polymerization, as appropriate, concern must also be given to the pot life or open times associated with such adhesive and sealant compositions, i.e., the period of time in which the adhesive or sealant is still workable. A short open time or pot life means that mating of the components must occur concurrent with or immediately following application of the adhesive or sealant. Further viscosity must also be properly addressed to ensure that the liquid adhesive and sealant materials do not run out of the bond interface and/or are capable of filling gaps often found with mated surfaces. While such one-part and two- or more part liquid adhesive and sealant compositions are broadly and successfully used in industrial manufacturing and assembly operations, their use is not without risk. Specifically, should an adhesive or sealant composition clog up the dispenser or, in the case of two- or more part systems, the mixing means improperly mix the components or fail to employ the proper mixing ratio of the components; it may be necessary to shut down the whole of the industrial assembly/manufacturing process until the problem is addressed. Additionally, whether or not the problem can be address on the run, i.e., while the process is still operating, all those substrates to which an improper adhesive or sealant has been applied will have to be scrapped or cleaned, if cleanable. Thus, there can be huge economic consequences should problems arise with the in-line use of hot melts as well as liquid adhesive and sealant compositions.
A second class of adhesives and sealants that have found use in industrial assembly and manufacturing processes are those known as pre-applied adhesives and sealants, i.e., those that are capable of being pre-applied to a substrate for later activation and use. Like liquid curable adhesives and sealants, pre-applied adhesives and sealants come in a number of chemistries and forms. The more common forms are the pressure sensitive adhesives and sealants, encased sealants and adhesives, encapsulated adhesive and sealants, and reactivatable adhesives and sealants. While each has their respective niche applications, they are not without their limitations and oftentimes one must compromise on performance and/or economics. Furthermore, they are not generally suited for use in high-speed industrial assembly operations, at least not without significant compromises or limitations.
Although pressure sensitive adhesives have found utility in a number of applications, including on stock materials, there are a number of limitations, both from a performance and utility standpoint. Generally, pressure sensitive materials do not provide the same bond strength or permanence as curable or polymerizable materials. This may not be a problem in certain applications, e.g., consumer envelopes; however, in applications requiring high bond strengths, it is an issue. Additionally, the use of pressure sensitive adhesives on stock materials requires added steps since a release paper or film must be applied over the pressure sensitive material to prevent pre-mature and/or unintended bonding and then removed prior to mating the surfaces to be bonded. These additional steps also necessitate added costs to the assembly operation in terms of materials, the release paper or film, and equipment needed to apply and remove the same. Though some pressure sensitive adhesives and sealants may be latently activatable, their activation means, e.g. heat or solvent, also limit their use as well as add costs.
Another form of adhesive and sealant compositions used in pre-applied applications are those wherein the adhesive or sealant composition or one or more components of the same are encased or encapsulated. Encased adhesives and sealants are those wherein a pool of a liquid curable or polymerizable composition is encased by a cured or polymerized film of the same or a second curable or polymerizable composition such that the liquid curable composition lies between the latter and the substrate to which it is applied. The encased systems are often anaerobic systems or heat activatable systems that incorporate a light activated component which, following application of the liquid curable or polymerizable composition to the substrate, are exposed to the appropriate light to effectuate a cure or polymerization of the top layer of the liquid composition thereby forming a skin on the surface of the liquid curable or polymerization composition. Alternatively, a liquid, film forming material, which may be curable, polymerizable or in solution, is sequentially applied as a separate over-layer to a substrate having a liquid polymerizable or curable adhesive or sealant composition already applied thereto and then exposed to conditions for effecting the cure or polymerization of the over-layer material so as to encase or skin over the first applied material. These type adhesive and sealant compositions are often found on threaded assemblies or more commonly in potting or encapsulating type applications, for example, of electronic components.
The most common form of pre-applied adhesive and sealant compositions are those known as the encapsulated or microencapsulated systems. Encapsulated systems typically comprise a plurality of microencapsulated curable or polymerizable adhesive or sealant components bound to the substrate by an appropriate binder composition. These systems may be of a single type of microcapsule wherein a curative necessary for effecting cure of the liquid curable or polymerizable composition is either entrained within or adhered to the microcapsule walls or is entrained in the binder and the liquid curable component contained in the microcapsules. Alternatively, there may be a plurality of microcapsules, each containing one or more components of the liquid curable or polymerizable composition provided that the ingredients necessary for initiating or effecting cure or polymerization are in separate microcapsules so that cure or polymerization is not effected until the microcapsules are broken and the contents thereof allowed to intermix and interact. Yet another microencapsulated adhesive or sealant system is that where the binder bonding the microcapsules to the substrate surface is actually the adhesive or sealant material and the microcapsules contain a solvent for the binder material. Upon rupture of the microcapsules, the solvent is released softening or dissolving the binder to allow for the mating of substrates and the solvent is subsequently absorbed into one or more of the substrates and/or evaporated off leaving the re-solidified adhesive or sealant.
Pre-applied encapsulated adhesives and sealants have utility in a number of applications, particularly in thread locking, snap fit and retaining applications where a threading action and/or interference fit provides the necessary action to fracture the microcapsules, thereby releasing and intermixing, as necessary, the components of the liquid curable adhesive or sealant composition. Such compositions and their applications are show in, for example, Wallace (U.S. Pat. No. 4,428,982), Müller et. al. (U.S. Pat. No. 4,100,954) Sweeney (U.S. Pat. Nos. 4,556,206 and 4,830,558), Rich et. al. (U.S. Pat. No. 5,853,520), Matsuo (U.S. Pat. No. 6,025,074), Bachmann et. al. (U.S. Pat. No. 3,814,156) and Bohli (U.S. Pat. No. 3,866,873).
They also find use in bonding or laminating flat sheets of one substrate to itself or another flat substrate where one or more pinch rollers, a stationary blade or other means, including finger pressure, compress the mated substrate surfaces with the pre-applied adhesive sandwiched in between whereby the compressive forces fracture the microcapsules and facilitate the intermixing of the components of the curable or polymerization compositions. For example, Akridge et. al. (U.S. Pat. No. 5,794,409) and Haugwitz (U.S. Pat. No. 4,961,811) teach paper bonding applications employing encapsulated adhesive compositions.
Although pre-applied adhesives and sealants have found broad commercial use, they are not without limitations and disadvantages. One of the key disadvantages or limitations of the encapsulated adhesive and sealant compositions lies in the fragility of the microcapsule walls. Consequently, the pre-application of such microencapsulated adhesives tend to be limited to those applications where there is little or limited opportunity for premature fracture of the shell wall. For example, where such materials are to be pre-applied to stock materials, storage and handling of the stock materials must be such that the areas to which the encapsulated adhesive or sealant is applied do not come in contact with each other, other substrates and/or are not subject to compressive forces. Stacking of stock materials, one on top of the other, may lead to premature fracturing of the microcapsules, thus leading to unwanted bonding of one stock material to another and, even if such bonding does not occur, consumes the liquid curable or polymerizable components in the ruptured microcapsules, leaving less, and oftentimes insufficient material for the ultimate bonding or sealing application. Similarly, when the microencapsulated adhesive is applied to small fasteners (e.g., screws, bolts, push pins and the like), because such products are often loosely packaged, they often bond to each other as a result of collisions between the products during packaging and handling.
Furthermore, in those automated assembly operations where a stock material having a pre-applied adhesive may come in contact with other substrates or the handling and assembling equipment, the potential exists for premature and unwanted bonding and/or consumption of liquid curable materials. In a high-speed assembly process, the last thing one wants is to have to shut down the assembly line to remove a bonded component. While such point contact bonded pieces may be readily parted, cured materials remain in the threads and/or on the surface of the substrate making proper threading or, in the case of an interference fit situation, insertion difficult, if not impossible. In other applications, such cured materials may act as a spacer between the substrates to be mated, thereby creating a gap where no gap is desired. Consequently, in each of these situations, it may be necessary to remove the cured materials before the item can be used.
Though a number of solutions exist for overcoming some of the foregoing difficulties and problems, they are not completely satisfactory or totally effective, if even practical. For example, while it is possible to individually package or to create special packaging that does not allow contact between the substrates carrying the pre-applied adhesives, such solutions are most often too expensive, particularly for high volume commodity applications such as small fasteners. Furthermore, besides the cost and need for materials and equipment to perform the proper packaging, such packaging may introduce the need for yet another apparatus in order to remove the particular substrate from the custom packaging for introduction into the assembly process. Similarly, special racks and/or spacer elements may be employed to keep stock materials from touching one another; however, again, costs are increased and production efficiencies may be adversely affected.
Problems with premature fracturing can also be mitigated or reduced by using thicker shell walls on the microcapsules and/or spacer particles; however, these have the disadvantage of increasing the amount of non-adhesive and non-sealing materials at the bond or seal interface. As more and more of the solid shell material is present or as solid particles are added to protect the weaker, microencapsulated liquid particles, there is less liquid curable component available to achieve the bond or seal for a given volume of the microencapsulated adhesive or sealant composition. Similarly, such “filler” materials will present additional problems in that they serve as a spacer between the substrates, even if no gap is present or desired. Additionally, in retaining and interference fit situations, e.g., the insertion of a pin into a cylindrical recess, the presence of such “filler” particles may prevent proper fitting of the substrates or cause the liquid curable adhesive or sealant material to be scraped off the one substrate as it is being inserted into the other. Consequently, in each of these circumstances, one may end up with weak bonds and/or poor seals.
Another limitation on the use of conventional pre-applied microencapsulated adhesive and sealant compositions in industrial applications relates to the viscosity of the encapsulated compositions, especially prior to cure or polymerization. Once the microcapsules containing the liquid components are ruptured, the liquid quickly runs across the surface. The tendency is for the same to form a monolayer except where capillary forces keep thicker amounts between substrates and/or the fractured shell materials. While this may not be a problem with applications where two substrates are to be mated concurrent with rupturing of the microcapsules, care must be given to ensure that too much run out or squeeze out does not occur, particularly where a gap may be present, e.g., where one or both substrates to be mated have an uneven surface and/or a flex which manifests itself once the rupturing forces are removed and the substrates relax to their normal position.
As noted above, pre-applied adhesives and sealants have found utility in a number of stock material applications; however, their use is limited due to the constraints of activation and, perhaps more commonly, the physical and/or performance characteristics of the typical pre-applied adhesives. In the latter case, due to poor or incomplete activation and/or availability of the curable components, pre-applied adhesives and sealants oftentimes manifest poor bond/seal strengths. Additionally, due to the constraints on encapsulating high viscosity materials, pre-applied adhesives tend to be of low viscosity, such that they may readily run out of or, during assembly and/or activation, are pressed or squeezed out of the bond interface. Furthermore, with concerns of capsule fragility and pre-mature breakage, the amounts of activators and catalyst and other cure speed enhancers are limited to prevent premature curing.
In order to overcome many of the shortcomings and problems associated with pre-applied encapsulated adhesives and sealants as well as other types of adhesives, particularly hot melt adhesives, on stock materials for use in industrial assembly operations, the industry has turned its attention away from hot melts and encapsulated adhesive and to what are typically referred to as reactivatable adhesives. These reactivatable adhesives, though “cured” in place on the stock material, can be reactivated upon exposure to sufficient energies of various types, especially ultrasound or near infrared radiation (NIR). Such materials and their use on stock materials are disclosed in, e.g., Gong et. al. (US 2003/0041963 A1; US 2004/0164134 A1; US 2004/0164135 A1 and US 2004/0166309 A1); Nowicki et. al. (US 2004/0163754 A1; US 2004/0163768 A1 US 2004/0166238 A1;) and Pierce et. al. (US 2004/0166257 A1). These materials, however, are limited in chemistries and, thus, applications. More problematic is the fact that they introduce a number of new problems, particularly health and safety problems. Specifically, these materials require specialized equipment not only for generating the NIR and ultrasound energies but also in protecting the workers and workplace from the energies so produced.
Thus, while conventional pre-applied adhesives have found considerable use in the manufacture of certain stock materials, their use is limited and not without its detractions. It would be desirable, therefore, to provide stock materials having a pre-applied adhesive wherein concerns relative to premature fracturing of the microencapsulated adhesive is greatly reduced, if not overcome. Similarly, it would be desirable to provide stock materials where concerns of premature bonding due to point contact or rough handling during processing, transportation and/or use is greatly reduced if not overcome. Furthermore, it would be desirable to expand the realm of stock materials to which pre-applied adhesive and sealant compositions could be applied, especially for high-speed assembly and manufacturing processes. In following, it would be desirable to provide pre-applied adhesive and sealant compositions whose cure speeds are immediate or close thereto. It would also be desirable to provide high-speed industrial assembly and manufacturing processes wherein the dispensing and application of liquid or flowable adhesives can be avoided. Finally, it would be desirable to provide a high-speed process by which a curable pre-applied adhesive or sealant composition on a stock material, which overcomes the aforementioned problems and issues, is activated quickly and with minimal complexity so as to be amenable for use in high-speed assembly and manufacturing processes.